Chapter 2 Flashcards
3 classifications of media
1) physical state - liquid, semisolid, soli
2) chemical composition - defined or complex
3) functional type (purpose)
Defined (synthetic) media VS complex media
- defined media: composition is precisely chemically defined; contain pure organic/inorganic compounds; exact formula
- complex media: one or more components is not chemically defined; contains extracts of animals, plants, or yeasts (blood, serum, meat extracts or infusions, milk, year extract, soybean digest, peptone)
General-purpose media
grow a broad spectrum of microbes; generally complex
Enriched media
contain complex organic substances (blood, serum, etc) or special growth factors for the growth of fastidious microbes
Selective media
contains agent(s) that inhibit the growth of a certain microbe or microbes; important for primary isolation of a specific type of microorganism
Differential media
allow multiple types of organisms to grow but display visible differences in how they grow (color, shape, gas production, etc)
Reducing media
contains a substance that absorbs O2 or slows the penetration of O2 (grow anaerobic bacteria)
Transport media
maintain and preserve specimens that have to be held for a period of time before clinical analysis
Carbohydrate fermentation media
contains sugars that can be fermented (converted to acids) with a pH indicator to show this reaction
Assay media
used by technologists to test the effectiveness of antimicrobial drugs
Enumeration media
used to count the numbers of organisms in a sample
What are the phases of magnification in light microscopy?
Real image: the initial image of the specimen formed by the objective
Virtual image: formed when the image is projected up through the microscope body to the plane of the eyepiece, the ocular lens forms a second image
What is resolution in light microscopy?
The capacity of an optical system to distinguish two adjacent objects or points from one another
What does oil immersion do in light microscopy?
uses oil to capture some of the light that would otherwise be lost to scatter, increasing resolution
what is the refraction index?
what measures contrasts
the degree of bending that light undergoes as it passes from one medium to another
the higher the difference in the RI, the sharper the contrast registered by the microscope and the eye
Bright-field microscope
- most widely used
- forms its image when light is transmitted through the specimen
- specimen absorbs some of this light and the rest is transmitted directly up through the ocular
Dark-field microscope
- a “stop” disk is added to a light-field microscope
- the stop blocks all light from entering the objective lens, except peripheral light that is reflected off the sides of the specimen itself
- produces brightly illuminated specimen surrounded by dark field
- used to see living cells that would be distorted by drying/heat of that cannot be stained with usual methods
Phase-Contrast microscope
- take advantage of the fact that cell structures differ in density
- devices that transform the subtle changes in light waves passing through the specimen into differences in light intensity
- produces greater internal detail
- useful for observing intracellular structures
Fluorescence Microscope
- furnished with a UV radiation source
- the dyes emit visible light when bombarded by short UV rays
- useful in diagnosing infections and pinpointing particular cellular structures
Confocal microscope
- uses a laser beam of light to scan various depths in the specimen and deliver a sharp image focusing on just a single plane
- able to capture a highly focused view at any level
- mostly used on fluorescently stained specimens
Transmission Electron Microscope (TEM)
- method of choice for viewing the detailed structure of cells and viruses
- produces its image by transmitting electrons through the specimen
- specimen must be sectioned into extremely thick slices and stained or coated with metals that will increase image contrast
Scanning Electron Microscope (SEM)
- provides dramatic and realistic images
- bombards the surface of a metal-coated specimen with electrons
- a shower of electrons deflected from the surface and the electron pattern is displayed as an image on a TV screen
- designed to create a detailed 3D view
positive stains
dye sticks to the specimen and gives it colour (usually basic bc they are positive and bacteria usually negative)
negative stains
does not stick to the specimen, but settles some distance from its outer boundary, forming a silhouette
Simple staining VS Differential staining
- Simple stairs: only require a single dye and an uncomplicated procedure
- Differential stains: uses 2 differently coloured dyes (primary dye and counterstain) to distinguish cell types or parts; more complex
Sequence of stains used in Gram staining
crystal violet (primary stain)
gram’s iodine (mordant)
an alcohol rinse (decolorizer)
a contrasting counterstain
What colours do gram-positive and negative produce?
gram-positive = purple gram-negative = red
Types of differential stains
gram stain, acid-fast stain, endospore stain
Types of special stains
capsular stains, flagellar stains
